Provide a resource of athymic nude mice for xenotransplantation of various human epithelial tissues and study the development of premalignant and/or malignant changes in response to in vitro and/or in vivo exposure to carcinogens. The contractor is responsible for maintaining a self-sustaining nude mouse breeding colony, establishing methods for xenotransplantation of various human tissue (bronchus, pancreatic duct, esophagus, colon, etc.) and for their subsequent in vivo exposure to carcinogens. Additionally, the contractor will assay for the tumorigenicity of human cells that have been experimentally manipulated in vitro. Technical support in the areas of routine histology, chemistry, immunology, and genetics are also provided.